Poisoning (or deactivation) of fluid catalytic cracking (FCC) catalysts is a persistent problem especially as petroleum refiners often work with hydrocarbon feedstocks which contain substantial amounts of vanadium and/or nickel. Premature catalyst deactivation leads to added refining cost both in terms of the amount of catalyst consumed and in terms of down time for the refinery.
In the past, various additives have been proposed to passivate poisoning metals such that their deactivating effect is lessened. Examples of compositions which have been proposed for this purpose include magnesium aluminate spinel (U.S. Pat. No. 5,057,205), hydrotalcite (U.S. Pat. No. 4,889,615), rare earth compounds in clay/alumina matrix (U.S. Pat. No. 5,304,299), rare earth compounds in acid-reacted metakaolin matrix (U.S. Pat. No. 5,248,642), co-precipitated non-spinel ternary oxides (U.S. Pat. No. 5,407,878), etc.
In general, the use of any additive may present issues for the refiner in practice. The additive content in the catalyst inventory may require separate monitoring. Additives may cause the creation of undesired effluents in the regenerator. Additives may require or create altered conditions in the FCC unit. Additives are often more expensive than the cracking catalyst itself. Thus, it is often desired to minimize the amount and/or number of additives used.
While known metals passivation additives often produce satisfactory results, there is a continued need for improved additives for metals passivation, especially additives which are more suitable for manufacture on a commercial scale.